JP2002304979A - Separator for alkaline battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin separator excellently passing an oxygen gas produced when overcharging an alkaline secondary battery, suppressing a pressure rise in the battery, and causing no short-circuiting in it. SOLUTION: After rugged parts are formed on the surface of a non-woven fabric of a thermoplastic resin, a polyorefine based resin in particular, in advance, hydrophilization treatment is applied to the non-woven fabric to obtain this separator for the alkaline battery. The separator for the alkaline battery is not short-circuited when assembling it in the battery, and the battery having this separator built-in has an excellent internal pressure suppressing effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sealed alkaline battery such as a nickel-hydrogen storage battery and a nickel-cadmium storage battery, and more particularly to a battery separator and a method of manufacturing the same.

[0002]

2. Description of the Related Art A sealed alkaline storage battery has a positive electrode, a negative electrode,
The positive electrode and the negative electrode are roughly divided into an electrolyte, a separator, and a container. The positive electrode and the negative electrode are separated by the separator, and are housed in the container while being immersed in the electrolyte solution.

In a sealed alkaline storage battery, a Neumann system is employed in which oxygen gas generated at the positive electrode during overcharge is absorbed by the negative electrode to prevent a rise in battery internal pressure. Therefore, since the internal pressure rise during overcharge is relatively small and the safety is high, applications for large current applications such as electric vehicles and power tools are being promoted. However,
During overcharge, if the generation rate of oxygen gas at the positive electrode becomes faster than the oxygen gas absorption rate at the negative electrode side, the internal pressure of the battery gradually increases, leading to destruction of the battery and shortening of the service life. Various studies have been made to make this possible.
In particular, with respect to the separator, studies are being made to smoothly transmit the generated oxygen gas from the positive electrode to the negative electrode.

On the other hand, as the capacity of a battery is increased, it is desired to reduce the thickness of the separator so that the volume occupied in the battery is reduced as much as possible. In this case, simply lowering the basis weight increases the probability of short-circuiting when forming the electrode group. Therefore, a method of increasing the fiber density has been studied. However, when the fiber density is increased in this manner, the space volume in the separator is reduced, and the gas permeability is reduced, so that there is a problem that the internal pressure of the battery is greatly increased.

In order to solve such a problem, for example, JP-A-10-106525 discloses a high-density layer on the side facing the positive electrode plate and a low-density layer having a lower fiber density than the high-density layer on the side facing the negative electrode plate. Non-woven fabric having a density layer, JP-A-6-11
No. 1847 discloses a fine fiber-containing layer (liquid retention layer) on the negative electrode side.
Non-woven fabric comprising a positive-fiber-side thick-fiber-containing layer;
No. 82115 discloses a nonwoven fabric in which an acrylic acid-containing fiber-containing layer and a polyolefin-based fiber-containing layer are heat-bonded and optionally subjected to a sulfonation treatment.
JP-A-7-57712 discloses a nonwoven fabric obtained by graft-polymerizing a hydrophilic monomer onto a nonwoven fabric in which a thick fiber-containing layer and a fine fiber-containing layer are integrated as described in JP-A No. 9-57712. Nonwoven fabric, JP-A-11-54
No. 101 discloses a multilayer nonwoven fabric produced by using a hydroentanglement treatment, and JP-A-5-89869 reports a battery in which an electrolytic solution-resistant net is provided between a separator and a negative electrode. I have. However, each method is characterized by overlapping a plurality of layers with different characteristics,
As a result, the thickness of the battery increases, which is not suitable for increasing the capacity of the battery. Further, the fibers present in the nonwoven fabric are entangled with each other, and there are many spaces (in other words, pores) in which gases and electrolytes of various sizes, which are created by the entanglement of the fibers, can move.
Here, the layer mainly composed of thick fibers or the low-density layer has a particularly large pore size (hereinafter, referred to as a pore diameter), and electrode active material particles that penetrate electrode burr or are released from the electrode are separated. There is also a drawback that it is buried in and short-circuited.

In general, when a non-woven fabric or other porous material is used as a separator for an alkaline battery, it is necessary to maintain affinity with an electrolytic solution for a long period of time, and a hydrophobic resin such as a polyolefin resin is used. When used, it is necessary to perform a hydrophilic treatment. Examples of the method of hydrophilization treatment include grafting treatment, sulfonation treatment, surfactant attachment treatment, corona treatment, plasma treatment, fluorine gas treatment, and resin coating treatment.
Above all, sulfonation by sulfuric acid treatment, fuming sulfuric acid treatment, or sulfur trioxide gas treatment, because it can maintain hydrophilicity for a long period of time and has a function of adsorbing impurities (ammonia) which is regarded as a problem in nickel-metal hydride batteries It is preferable to perform at least one of the treatment and the graft treatment of a monomer having a hydrophilic functional group represented by acrylic acid. It is also good to combine the sulfonation treatment or the grafting treatment with another hydrophilic treatment.

However, at least when forming irregularities on the non-woven fabric subjected to the sulfonation treatment, it is necessary to fuse the fibers by heat. Therefore, the battery incorporated by removing the sulfonic acid group formed on the surface of the non-woven fabric is required. It has been found that there is a problem that the performance is lowered, or the yield at the time of manufacturing the battery is deteriorated due to the reduction in strength that occurs simultaneously with the elimination of the sulfonic acid group.

On the other hand, the nonwoven fabric subjected to the grafting treatment has an increased heat capacity, so that it is difficult to form irregularities after the grafting treatment, and at the same time, even if the irregularities are formed under severe conditions, it is the same as in the case of the sulfonation treatment. It has been found that there are problems such as a decrease in battery performance due to elimination of a functional group and a decrease in strength.

[0009]

DISCLOSURE OF THE INVENTION In view of the above problems, the present inventors have successfully passed oxygen gas generated at the time of overcharging of an alkaline secondary battery, making it difficult for the internal pressure of the battery to rise.
With the aim of obtaining a thin separator that does not cause a short circuit, the present inventors have conducted intensive studies on the raw material and shape of the nonwoven fabric and the method for hydrophilizing the same, and have invented a separator satisfying the above object and a method for producing the same.

[0010]

That is, the present inventors have prepared a non-woven fabric made of a thermoplastic resin, particularly a polyolefin resin, and formed irregularities on the surface thereof before the hydrophilization treatment, and then formed the non-woven fabric on the non-woven fabric. By performing the hydrophilic treatment, to obtain a hydrophilic treated separator having irregularities on the surface, when the separator is incorporated into a battery, an alkaline battery separator characterized by having an excellent internal pressure suppression effect To provide.

The depth of the recess according to the present invention is 5% or more and 50% or less with respect to the apparent thickness of the separator, and the area of the recess is 5% or more and 50% or less with respect to the entire area of the separator. The present invention relates to an alkaline battery separator and a method for producing the same.

Further, the present invention relates to the above-mentioned separator for an alkaline battery, wherein the thermoplastic resin is a polyolefin resin, and a method for producing the same.

The average fiber diameter of the nonwoven fabric constituting the separator is in the range of 1 to 20 μm, the basis weight of the nonwoven fabric is in the range of 20 to 75 g / m ² , and the air permeability of the nonwoven fabric is 2 to 50 cm ^3. / Cm ² / s, the thickness of the non-woven fabric is 180 μm or less, and the puncture strength of the non-woven fabric is 5 N or more, and a method for producing the alkaline battery separator.

[0014] The present invention also relates to an alkaline battery using a battery separator, wherein the surface having irregularities of the separator faces at least the negative electrode.

[0015] The present invention also relates to a method for producing a separator for an alkaline battery, characterized in that the above-mentioned hydrophilic treatment is at least one of a sulfonation treatment and a graft treatment.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION As a specific method, first, in the battery separator of the present invention, it is desirable that the form is a non-woven fabric, but other than that, a porous body such as a woven fabric or a knitted fabric is used. A fiber sheet, a fiber aggregate, a high-density woven or knitted fabric, a foam-type porous body, or the like can be used favorably similarly to a nonwoven fabric.

When a non-woven fabric is used as the battery separator of the present invention, any known method can be used for its production. For example, a non-woven fabric made of long fibers manufactured by a spun bond method can be used. A nonwoven fabric formed by a melt-blowing method or flash spinning can be used, and a method called air-laying, in which the opened fibers are carried by an air stream, can also be used. Further, a chemical bonding method in which a dry nonwoven fabric represented by a card method is bonded with an adhesive, and a thermal bonding method in which self bonding or bonding fibers are used to bond the nonwoven fabric can be used. Further, as a confounding method, there are a spunlace method using a high-pressure water flow, a needle punch method in which the web is needled with a special needle, a stitch bonding method in which yarn is knitted, and the like. Can be used in things. Further, a nonwoven fabric produced by making a fiber by wet method and using the same fiber bonding and fiber entanglement method as the method shown in the dry method can also be used.

Although any organic resin material can be used as the resin constituting the battery separator of the present invention, it is preferable to use a polyolefin resin from the viewpoints of resistance to an electrolytic solution and oxidation resistance. Here, the polyolefin resin is a resin composed of a polyolefin alone or a resin composed of a copolymer of an olefin and another monomer. Examples of the polyolefin include polyethylene, polypropylene, polymethylpentene, and polybutene. , Polyethylene-propylene, polyethylene-butene-propylene, and the like, and other monomers copolymerizable with the olefin include styrene, vinyl butyrate, and vinyl acetate.

The above-mentioned resin may be used alone, or a core-sheath type conjugate fiber, an eccentric body-sheath type conjugate fiber, a parallel type conjugate fiber,
Two or more kinds of resins may be mixed, such as sea-island composite fibers and splittable composite fibers, and are not particularly limited. For example, a nonwoven fabric made of a core-sheath conjugate fiber in which polyethylene is arranged on the outside of polypropylene or a mixture thereof can be effectively used.

The resin component may have any molecular weight, from low molecular weight to ultra-high molecular weight, either singly or as a mixture.
For example, it is very effective to mix high-strength fibers produced using an ultrahigh molecular weight resin.

In addition to these resins, various additives such as an antioxidant, an ultraviolet ray inhibitor, an antistatic agent, a coloring agent, a flame retardant, and a metal component may be mixed. The addition amount may be within a range that does not lower the battery performance when the battery is finally incorporated into the battery.

In the nonwoven fabric prepared using the above-described thermoplastic fiber, the average fiber diameter is preferably in the range of 1 to 20 μm, and more preferably in the range of 2 to 15 μm. If the fiber diameter is less than 1 μm, the fiber strength is essentially low, and short-circuiting occurs during battery production. On the other hand, when the fiber diameter exceeds 20 μm, the portion having a large pore diameter increases when the nonwoven fabric is used, which leads to a short circuit.

In the nonwoven fabric in the above range, the air permeability is preferably 50 cm ³ / cm ² / s or less, more preferably 30 cm ³ / cm ² / s by the Frazier method.
Hereinafter, more preferably 25 cm ³ / cm ² / s. In the case of a nonwoven fabric having an air permeability measured by the Frazier method that is equal to or more than the above range, a portion having a large pore diameter increases and a short circuit occurs. Furthermore, in order to ensure the permeability of oxygen gas generated at the end of charging, the air permeability by the Frazier method is 2 cm ³ / cm ² /
s or more, more preferably 4 cm ³ /
cm ² / s or more. Therefore, it is desirable that the air permeability of the nonwoven fabric used in the present invention is in the range of ^{2 to} 50 cm ³ / cm ² / s.

Further, in order to produce a nonwoven fabric having the above fiber diameter and air permeability, the basis weight of the nonwoven fabric needs to be 20 g / m ² or more and 75 g / m ² or less, and most preferably 25 g / m ^2. It is preferably at least 60 g / m ² ,
More preferably, it is 30 g / m ² or more and 55 g / m ² or less. If the basis weight of the nonwoven fabric is greater than 75 g / m ² , the nonwoven fabric is too clogged and the air permeability becomes 2 cm ³ / cm ² / s or less. Conversely, when the basis weight of the nonwoven fabric is less than 20 g / m ² ,
Since the strength is essentially low, the separator is likely to be short-circuited.

In the separator of the present invention, the unevenness of the nonwoven fabric needs to be performed before the hydrophilic treatment step. If processing is performed after the hydrophilic treatment step, as described above, the functional group that has modified the fiber surface during the hydrophilic treatment is eliminated, leading to a decrease in battery performance and also a decrease in strength.

The method of providing the unevenness is not particularly limited, and any known method for forming the unevenness can be used. For example, pressing with an embossing roll or gear roll, pressing with a mold or metal mesh, resin net, etc., transferring the unevenness, cutting with a sharp blade, etc., squeezing or rubbing, having unevenness Examples of the method include a method of forming a nonwoven fabric on a net and a method of partially melting and compressing or removing a resin.

The cross-sectional shape of the concavities and convexities formed by the above-mentioned concavo-convex processing may be any of a U-shape, a V-shape or a square shape as shown in FIG. Further, the shape of the concavo-convex viewed from the upper surface may be continuous or discontinuous such as a groove or a ridge, and these may be used alone or in combination. Examples of the continuous unevenness include those arranged in one direction as shown in FIG. 2 and those which intersect at a lattice or randomly. Non-continuous ones include polygons such as a circle, a star, a triangle, a square, and a cross as shown in FIG. 3, irregular shapes, and combinations thereof, and are not limited. It should be noted that those having continuous grooves on the surface are particularly effective. Further, it is preferable that the irregularities are uniformly dispersed.

Due to the irregularities provided by the above method, a minute space can be formed between the negative electrode and the separator when the battery is wound. Oxygen gas generated at the positive electrode passes through the separator, is temporarily held in this space, and is then consumed on the negative electrode surface, thereby suppressing an increase in battery internal pressure. Therefore, in the present invention, the unevenness needs to be such that a sufficient minute space can be formed between the separator and the electrode surface in the battery.

In the alkaline battery separator of the present invention, it is necessary to apply a hydrophilic treatment after forming the unevenness on the surface of the nonwoven fabric. If the irregularities are formed after the hydrophilic treatment, the separation of the hydrophilic functional groups and the strength of the nonwoven fabric are reduced, so that an excellent separator cannot be obtained.

As a method of the hydrophilic treatment, it is preferable to carry out either a graft treatment or a sulfonation treatment. Further, a surfactant attachment treatment, a corona treatment, a plasma treatment, a fluorine gas treatment, a resin coating treatment, or the like may be performed in combination.

As the sulfonation treatment method, a method of dipping in hot sulfuric acid, a method of dipping in fuming sulfuric acid, a method of dipping in chlorosulfuric acid, a method of contacting with sulfur trioxide gas, a dipping in sulfuric acid or fuming sulfuric acid Method of contacting with sulfur trioxide gas or sulfur dioxide gas repeatedly, method of contacting with sulfur trioxide gas after immersion in hot sulfuric acid, method of contacting with mixed gas of sulfur dioxide and oxygen after performing fluorine treatment Any of these can be suitably used. As the grafting method, any known method such as a method of applying energy such as a UV irradiation treatment, a plasma treatment, a corona treatment and the like using a catalyst at the same time as bringing a vinyl monomer into contact with a resin may be used. It is possible.

When the above-mentioned hydrophilization treatment is used, it is necessary to make the surface of the nonwoven fabric uneven, and then perform the hydrophilization treatment. For example, when forming irregularities on a non-woven fabric subjected to sulfonation, it is necessary to fuse the fibers by heat, so that the performance of the incorporated battery is reduced due to the elimination of sulfone groups formed on the non-woven fabric surface. This is not desirable because there is a problem that the yield at the time of battery production is deteriorated due to a decrease in strength that occurs simultaneously with the elimination of the sulfone group. Also,
The grafted nonwoven fabric has an increased heat capacity, which makes it difficult to provide irregularities after the grafting process. It is not desirable because there are problems such as a decrease in battery performance due to desorption and a decrease in strength. Also, the case where unevenness is formed after a surfactant or resin coating treatment is not desirable because it has the same problem as the graft treatment due to moisture adsorption by the surfactant and adhesiveness of the coating resin.

By performing the above-described hydrophilic treatment, hydrophilic functional groups such as sulfonic acid groups, carboxyl groups, carbonyl groups, hydroxyl groups, and fluorine functional groups can be provided on the fiber surface. In addition, the amount of the hydrophilic functional group is preferably at least 0.005 meq / g or more when evaluated from the amount of ion exchange. If the amount of ion exchange is smaller than that, the affinity with the electrolyte is expected to be low. Can not. on the other hand,
If the hydrophilicity is too high, the strength of the nonwoven fabric is reduced in the sulfonation treatment, and the life of the graft treatment is shortened when incorporated into a battery. Therefore, in the sulfonation treatment, the amount of sulfur determined by emission spectroscopy was 4%.
Should be below 0000 ppm. Further, in the grafting treatment, the weight increase due to the grafting treatment should be suppressed to 40% by weight or less.

As described above, in the separator obtained by hydrophilizing the uneven nonwoven fabric, the depth of the recess is 5% to 50% of the apparent thickness of the separator.
% Or less, more preferably 10% or more and 50% or less. If the depth of the recess is less than 5%, no sufficient space is formed between the electrode surface and the separator, and the effect of the unevenness cannot be obtained. Further, when the depth of the concave portion is larger than 50%, an extremely thin portion is formed, so that the strength of the portion is reduced and a break or a short circuit at the time of winding the battery is easily caused. In order to avoid this, if the thickness of the recess is increased,
The thickness of the entire separator increases.

The area of the recess with respect to the entire area of the separator is preferably in the range of 5% to 50%. If it is less than 5%, the effect of providing unevenness cannot be obtained,
On the other hand, if it is more than 50%, the adhesion to the electrode is poor, and the battery performance is reduced.

When a battery is formed using the separator according to the present invention, it is necessary to arrange the battery so that the surface having irregularities faces at least the negative electrode. By arranging the irregularities on the negative electrode side, a space is formed between the negative electrode surface and the separator, and oxygen gas generated from the positive electrode can efficiently move to the negative electrode side. It is well absorbed, and as a result, an increase in the internal pressure of the battery is suppressed.

When a sealed battery is produced using the separator of the present invention, (1) pressure and tension applied to the separator when producing a wound body, (2) flatness of the electrode surface, (3) ) Electrode hardness, (4) Electrolyte volume, (5) Electrolyte injection method, (6) Concentration of resistance to stress and irregularities on removal of core from wound body, (7) Tab welding In doing so, it is necessary to consider at least the temperature applied to the separator. Here, if the pressure or tension applied to the separator when producing a wound body is high, the unevenness existing on the separator surface is crushed, and the effect of suppressing the internal pressure is reduced. In some cases, a short circuit occurs. Further, poor flatness of the electrode surface leads to a short circuit. On the other hand, if the electrode is too soft, the irregularities will be buried and the effect of suppressing the internal pressure will be weakened. If the amount of the electrolyte used is too large, the internal pressure tends to increase, and if the amount is small, the internal resistance increases and the life of the battery is shortened. In addition, if the method of injecting the electrolyte is bad, the productivity of the battery deteriorates, and the performance of the battery varies because the electrolyte is not uniformly distributed. In addition, if the resistance at the time of removing the winding core from the wound body is large, or if stress concentration occurs on the uneven portion, the separator is broken and short-circuited. In addition, if the separator is heated and melted or shrunk when welding the tab required for removing the battery from the electrode, a short circuit may occur.
Therefore, when manufacturing a battery using the separator of the present invention, it is necessary to consider at least the points that are problematic when manufacturing such a battery. Included in the scope of the battery of the invention. It is also preferable to consider the shape of the battery, the ratio between the electrode and the separator, the alloy composition used for the electrode, the winding method, and the like.

In the separator manufactured under the above conditions, when measured by an evaluation method described below,
Sufficient gas permeability and separator strength can be imparted with a thickness of 50 μm, and good gas permeability is obtained even with a thin separator of about 60 to 120 μm whose fiber density is relatively high to prevent short circuit. Properties can be maintained, and an increase in internal pressure can be suppressed.

Further, since the gas permeability can be maintained even when the fiber density is increased, the separator having a puncture strength of 5 N or more involved in the short-circuit suppression performance of the battery, and furthermore, 8 N
It is possible to produce a separator of 10N or more.

Hereinafter, methods for measuring the physical properties of various separators according to the present invention will be described.

· Weight, apparent thickness, depth of recess (1) A test piece (width 5 cm, length 10 c)
m) was collected, and the value converted to the weight per 1 m ² based on the weight when dried at 60 ° C. ± 2 ° C. for 10 hours,
The basis weight was [g / m ² ]. The test piece n was determined by averaging 20 points. (2) The thickness at the center of the test piece was measured to have a diameter of 31.
5mm digital thickness gauge (Peacock digital thickness gauge)
It measured using. An average of n = 20 points was determined. (3) The cross-sectional shape of the separator is magnified 300 times with an optical microscope, and the thickness of the concave portion is measured. The difference between the recess thickness and the apparent thickness was defined as the recess depth. The average was obtained at n = 30 points.

Air permeability According to the air permeability measurement method of JIS L1096-1990,
It was measured by a Frazier type testing machine.

Tensile strength Using a sample having a width of 5 cm and a length of 15 cm,
The tensile strength in the direction D) is determined according to JIS L1068.
According to the (test method for tensile strength of woven fabric), the gripping interval should be 10
The measurement was carried out at a pulling speed of 30 cm / min. The test piece n was determined by averaging 20 points.

Puncture strength The puncture strength was determined by measuring the sample at a diameter of 1.128 cm and an area of 1 c.
fixed to the circular hole holder m ^2, tip spherical 0.5 R,
The maximum load applied to the needle when the needle having a diameter of 1 mmΦ was lowered at a speed of 2 mm / sec until it penetrated the sample was determined. Specifically, Kato Tech Co., Ltd. KES-
The measurement was performed using a G5 handy compression tester. The test piece n was determined by averaging 100 points.

Amount of ion exchange A 0.2 g test piece was completely impregnated with a 1 mol / L HCl aqueous solution, and then transferred to a 1 mol / L HCl aqueous solution and immersed for 1 hour. Then, the pH is 6 ~
Washed several times until 7. Next, it was dried for 2 hours by a blow dryer at 60 ° C. and cooled to room temperature. The cooled test piece was immersed in a 0.01 mol / dm ³ KOH aqueous solution (100 cm ³⁾ and shaken at 45 ° C. for 1 hour. Then, the test piece was taken out, and a solution (25 cm ³⁾ was collected. Neutralization titration was performed with an aqueous HCl solution. The blank solution was titrated in the same manner, and the amount of potassium ion exchange was calculated from Equation 1.

Ion exchange amount (meq / g) = {(V0−V1) × 100 × 0.01 × f} / (25 × 0.2) (Equation 1) where V1: required for titration of sample HCl aqueous solution (c
m ³ ) V0: Amount of HCl aqueous solution required for titration of blank solution (c
m ³ ) f: Factor of HCl aqueous solution

Discharge capacity ratio, battery internal pressure First, a paste-type nickel hydroxide positive electrode, a paste-type hydrogen storage alloy negative electrode, and a separator were spirally wound, and SC
A sealed battery of a size (capacity 2500 mAh) is prepared. Note that an aqueous solution of potassium hydroxide to which lithium hydroxide is added is used as an electrolyte for this battery.

As an initial activation process for preparation, the substrate is kept at 45 ° C. for 6 hours. Thereafter, the battery is charged at 0.2 C for 6 hours in an air atmosphere at 20 ° C., discharged at 0.2 C (discharge end voltage: 1.0 V), and this charge / discharge operation is repeated 10 times. The ratio of the 10th discharge capacity to the theoretical capacity was defined as the discharge capacity ratio of this battery. The above-mentioned 0.2C discharge is to discharge a densely charged battery in 5 hours, and at this time, the current value of the discharge is set to an appropriate value.

The activated battery was charged at 0.5 C for 3 hours at an ambient temperature of 20 ° C. (charging depth 1
50%), and the internal pressure of the battery was measured.

[0050]

EXAMPLES The present invention will be specifically described below with reference to examples of the present invention, but the present invention is by no means limited to these examples.

Example 1 A non-woven fabric made of a core-sheath composite fiber having commercially available polypropylene as a core component and polyethylene as a sheath component (Nippon Kodoshi Paper Industries WPSD40120; average fiber diameter 12 μm, basis weight 40 g)
/ m ² ) with a 7% convex area ratio (roll temperature 12)
(0 ° C.) and a flat roll made of stainless steel at 120 ° C., and pressurized at a linear pressure of 3.4 MPa to form a groove-shaped recess only on one surface. This is added to fuming sulfuric acid at 60 ° C and 20%
After immersion treatment for a minute, washing with concentrated sulfuric acid, dilute sulfuric acid aqueous solution and ion-exchanged water was performed, followed by drying at 75 ° C to obtain a separator. Table 1 shows the various physical properties of the separator, and the discharge capacity ratio and the internal pressure during charging of a battery used with the concave surface of the separator facing the negative electrode.

Example 2 Commercially available polypropylene non-woven fabric (Nippon Kodoshi SLF5
0120, an average fiber diameter of 12 μm, and a basis weight of 50 g / m ² ) were pressed at a linear pressure of 3.4 MPa with a gear roll (roll temperature: 130 ° C.) having a convex area ratio of 15% and a stainless flat roll at 130 ° C. A groove-shaped concave portion was formed only in. This was prepared from 20% by weight of acrylic acid, 76.7% of distilled water, 0.2% by weight of benzophenone, 0.1% by weight of ferrous sulfate, and 3.0% by weight of nonionic surfactant, which had been saturated with nitrogen gas in advance. For 10 minutes. After removing the excess solution from this polyolefin nonwoven fabric, UV irradiation with a low-pressure mercury lamp is performed for 5 minutes,
Acrylic acid was graft polymerized. Next, after performing washing with pure water several times, it was dried at 75 ° C. to obtain a separator.
Table 1 shows various physical properties of the separator, and a discharge capacity ratio and a charging internal pressure of a battery used with the surface of the separator having the concave portion facing the negative electrode.

Example 3 A commercially available polypropylene nonwoven fabric (Nippon Kodoshi SLF)
50120, average fiber diameter 12 μm, basis weight 50 g / m ² )
Was subjected to a pressure treatment using an embossing roll heated to 135 ° C. and having a projection area ratio of 30% and a flat roll made of stainless steel at 120 ° C., and a dot-shaped concave portion was formed only on one surface. This was treated at 130 ° C. for 5 minutes using 96% sulfuric acid. After washing with a dilute sulfuric acid aqueous solution and ion-exchanged water, drying was performed at 75 ° C. to obtain a separator. Table 1 shows various physical properties of the separator, and the discharge capacity ratio and the internal pressure during charging of the battery using the separator.

Example 4 A polypropylene nonwoven fabric (Toyobo; thickness 180 μm, average fiber diameter 7 μm, basis weight 65 g / m ² ) produced by a melt blow method was embossed with a convex area ratio of 40% (roll temperature 140 ° C.). And a flat roll made of stainless steel at 140 ° C., and pressurized at a linear pressure of 3.4 MPa to form a groove-shaped concave portion only on one surface. 96%, 130
After immersion treatment in concentrated sulfuric acid at 5 ° C. for 5 minutes, washing with a dilute sulfuric acid aqueous solution and pure water, drying at 75 ° C. was performed to obtain a separator. Table 1 shows various physical properties of the separator, and a discharge capacity ratio and a charging internal pressure of a battery used with the surface of the separator having the concave portion facing the negative electrode.

[0055]

Comparative Example A comparative example of the present invention is shown below. According to a method not included in the scope of the present invention, it is not possible to obtain the excellent characteristics described in the text.

Comparative Example 1 In Example 1, after a fuming sulfuric acid treatment and a washing and drying treatment were performed first, a wire was formed with a gear roll (roll temperature: 120 ° C.) having a convex area ratio of 7% and a stainless flat roll at 120 ° C. At a pressure of 3.4 MPa, an attempt was made to form a groove-shaped recess only on one surface. However, in the nonwoven fabric subjected to the fuming sulfuric acid treatment first, fusion between the fibers was difficult, and the formation of the concave portion did not occur. Therefore, the linear pressure of the roll was increased to 5.0M.
When the pressure was changed to Pa, the concave portion was formed, but the pressed portion became black and became brittle. Table 1 shows various physical properties of the separator. When this separator was incorporated in a battery, all of the separators were broken or short-circuited at the time of winding, and the battery could not be obtained.

Comparative Example 2 In Example 2, after performing the grafting treatment and the washing and drying treatment, a linear pressure of 3.% was applied by a gear roll (roll temperature: 130 ° C.) having a projection area ratio of 15% and a stainless steel flat roll at 130 ° C. A pressure was applied at 4 MPa, and an attempt was made to form a groove-shaped recess only on one surface. However, almost no recess could be made. Table 1 shows various physical properties of the separator, the discharge capacity ratio of the battery using the separator, and the internal pressure of the rechargeable battery.

Comparative Example 3 In Comparative Example 2, the temperature of the gear roll was set to 170 ° C., and a concave portion was formed only on one surface. Although the concave portion was formed, discoloration of the pressurized portion also occurred, indicating deterioration of the functional group. Table 1 shows various physical properties of the separator, and the discharge capacity ratio and the internal pressure during charging of the battery using the separator.

Comparative Example 4 The same nonwoven fabric as in Example 4 was subjected to a sulfuric acid treatment and a washing and drying treatment, and then, using a gear roll having a convex area ratio of 15% (roll temperature: 120 ° C.) and a stainless steel flat roll at 120 ° C. By applying a linear pressure of 5.0 MPa, a groove-shaped concave portion was formed only on one surface. As in Comparative Example 1, the pressed portion was blackened and weakened. However, since the basis weight was high, one out of eight pieces could be incorporated into the battery without short-circuiting. Table 1 shows various physical properties of the separator, and the discharge capacity ratio and the internal pressure during charging of the battery using the separator.

[0060]

[Table 1]

While the internal pressure of the battery was suppressed in the separators of Examples 1 to 4, the effect of suppressing the internal pressure was not observed in the separator of Comparative Example 2. This is because the properties of the fiber surface were changed by the grafting treatment, and a concave portion could not be formed. Therefore, the depth of the concave portion was insufficient, and a sufficient space was not formed between the separator and the negative electrode surface.

In Comparative Example 1, all the batteries were short-circuited or broken when the batteries were wound. Further, also in Comparative Example 4, up to 7 out of 8 pieces were short-circuited or broken. This is because the heating of the sulfone group accelerated fiber deterioration and caused a decrease in strength when producing unevenness in the nonwoven fabric subjected to the sulfonation treatment. On the other hand, in the separators of Examples 1 to 4, the battery can be wound without causing breakage or short circuit.

In Comparative Examples 3 and 4, the increase in battery internal pressure was suppressed, but the discharge capacity ratio was low. This is because the unevenness was forcibly formed on the nonwoven fabric to which the functional group was imparted, so that the functional group deteriorated and began to dissolve in the electrolytic solution when incorporated into the battery, causing an increase in the internal resistance of the battery and a decrease in the electrode activity. It is considered that

As described above, the battery separator and the alkaline battery according to the present invention have been specifically described with reference to the examples. However, the present invention is not necessarily limited to the above examples. It is also possible to carry out the present invention with appropriate modifications within a compatible range, and all of them are included in the technical scope of the present invention.

[0065]

As described above, in the battery separator manufactured by the manufacturing method of the present invention, a minute space can be formed between the separator and the surface of the negative electrode. Oxygen gas accumulates,
The oxygen gas absorption reaction on the surface of the negative electrode proceeds smoothly, and it is possible to effectively suppress an increase in battery internal pressure during overcharge. Therefore, an alkaline battery using this separator has excellent safety.

[Brief description of the drawings]

FIG. 1 is an example of a cross-sectional shape of unevenness.

FIG. 2 is an example of an uneven portion viewed from above (in a continuous case)

FIG. 3 is an example of the uneven portion viewed from above (in the case of discontinuity)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 2/16 H01M 10/30 Z 10/30 D06M 7/02 A (72) Inventor Naohiko Takimoto Otsu, Shiga 2-1-1, Ichikatada F-term in Toyobo Co., Ltd. Research Laboratory (Reference) 4L031 AB34 BA13 BA17 DA08 4L033 AB07 AC07 CA18 CA70 4L047 AA14 AA27 AB07 CA12 CA19 CB01 CB08 CC12 5H021 AA06 BB04 BB09 EE02 EE04H01 H03H03 5H028 AA01 BB04 BB10 EE10 HH00 HH01 HH05

Claims (6)

[Claims] 1. A separator for an alkaline battery, wherein a non-woven fabric made of a thermoplastic resin having irregularities formed on at least one surface has been subjected to a hydrophilic treatment in advance. 2. The method according to claim 1, wherein the depth of the recess is from 5% to 50% of the apparent thickness of the separator, and the area of the recess is from 5% to 50% of the total area of the separator. The separator for an alkaline battery according to claim 1. 3. The alkaline battery separator according to claim 1, wherein the thermoplastic resin is a polyolefin resin. 4. The nonwoven fabric constituting the separator has an average fiber diameter in the range of 1 to 20 μm, and the basis weight of the nonwoven fabric is 2 μm.
0-75 g / m ² and the air permeability of the nonwoven fabric is 2
In the range of ~50cm ³ / cm ² / s, and the thickness of the nonwoven fabric is less than 180 [mu] m, and piercing strength for an alkaline cell according to any one of claims 1 to 4, characterized in that at least 5N Separator. 5. An alkaline battery using the alkaline battery separator according to claim 1, wherein a surface of the separator having irregularities faces at least the negative electrode. 6. The method for producing an alkaline battery separator according to claim 1, wherein at least one of a hydrophilization treatment and a sulfonation treatment or a graft treatment is performed.